Electricity Cost Calculator
Estimate the energy an appliance uses and what it costs, from its power, how long it runs and your price per kWh.
Worked example
A 1,000 watt heater used for 2 hours uses 1 kW × 2 h = 2 kWh. At 0.30 per kWh, that costs 0.60. If you did the same every day, it would come to 14 kWh over 7 days.
How we calculated this
Energy in kilowatt hours is the power in kilowatts multiplied by the time in hours. Watts are divided by 1,000 to give kilowatts, and minutes are divided by 60 to give hours. The cost is the energy multiplied by the price per kilowatt hour that you enter.
The daily rows repeat the usage you entered every day for 7, 30 and 365 days.
A result written as a plain number is exact. A result starting with “≈” has been rounded to 10 significant figures, because its exact decimal never ends or is too long to read comfortably. When an exact value is long, its full digits are shown underneath. The calculation itself is never rounded: only the display is.
What this result means
The result is the energy used in kilowatt hours and its estimated cost, using the power, time and price per kWh you entered.
Common mistakes
- Entering a price in pence and reading the cost as pounds. The cost is in the same unit as the price you type.
- Using the maximum power on the label for an appliance that only draws that much some of the time.
Assumptions and limitations
- It assumes the appliance draws the power you entered for the whole time. Many appliances, such as fridges, draw less on average.
- The daily rows repeat one day of usage and are an assumption, not a forecast. Standing charges are not included, and no tariffs are looked up.